Background Data on the
Photovoltaic Effect



The photovoltaic effect is in essence a direct conversion mechanism that converts light photons into electrical power. Light was considered for many years as a wave propagation phenomenon similar to radio frequency waves and other electromagnetic waves. In the beginning of the 20th century it was realized that light can also be described as elementary particles called photons (hence the "photo" prefix of the word photovoltaic). Voltaic is derived from the name Alessandro Volta who was pioneering in the late 1880s the electrical cells research (the predecessor of the modern battery). As a tribute to this great man, the electrical engineering term voltage is called after him. The photovoltaic history is fascinating, it went a long way in a relatively short time from a research topic to a big industry

What is the photovoltaic effect?

Sun light is a stream of photons. When photons hits the photovoltaic cell, part of them are reflected back, some are absorbed, and some goes through and comes out the other side. When a photon is absorbed, the energy of the photon is transferred to an electron in an atom of the photovoltaic cell. (the cell is thin sheet of a semiconductor material). The electron is therefore boosted with more energy, and can "jump" out from its orbit around the atom nucleus. The electron becomes a "free electron". (it leaves an "hole" were it was)

Many more free electrons are generated by the many photons that strike the cell. They all go into one direction (it is a photo diode), and can produce measurable current on an external load. (the free "holes" go the opposite direction)

Photovoltaic Cell Efficiency

You've might heard about efficiency; efficiency is a measure of the ratio between the electrical power that was generated in the solar cell and the photons power that hitted the cell. You've already saw two waste mechanisms - the photons that were reflected and the photons that went through.(only the absorbed photons did a useful job). There are other reasons for waste of energy in a practical cell... The leading edge research is in the direction of improving the efficiency and in reducing the manufacturing cost.

The cell, like a battery is capable of generating Direct Current (DC). Therefore, in cases the ultimate loads are expecting alternate current (AC) a DC to AC inverter is required to convert the DC power to AC power. All residential power in the US is AC, 110V 60Hz. In Europe the residential AC power is 230V 50Hz

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